A Formal General Method for the Synthesis of Spiroacetals: Easy Access to Oleocaran/Elmonin Core

Abstract

A general method for the synthesis of spiroacetals was investigated. Simple symmetrical [n,n]‐spiroacetals (n = 5,6) can be prepared from α,ω‐alkanediols by their conversion to the respective ω‐benzyloxyalkyl bromides, addition of their Grignard reagents to ethyl formate, further oxidation of the resulting secondary alcohols and finally deprotection with spontaneous intramolecular acetalization. Access to the respective unsymmetrical [m,n]‐spiroacetals (m,n = 5,6,7) was similarly achieved by addition of the above Grignard reagent to a ω‐benzyloxyalkanal, followed by the same reaction sequence. This method was further adapted for the synthesis of the unsubstituted structural core of natural spiroacetals oleocaran and elmonin, thus demonstrating its potential.